The present invention relates generally to the delivery of digital video using the well known MPEG-2 compression scheme, and more particularly, to a system and method for maximizing bandwidth efficiency by combining a number of digital video streams into one aggregate stream.
The delivery of digital video signals to a subscriber has been accomplished via many ways. For example, compressed digital video using the motion picture experts"" group (MPEG-2) compression/decompression methodology can be delivered using a variety of media including coaxial cable, fiber optic cable and satellite. Some of these delivery systems are considered xe2x80x9cvideo-on-demand,xe2x80x9d or xe2x80x9cnear video-on-demandxe2x80x9d in that a user, or subscriber, may select from a plurality of offerings and view a particular program as desired from time to time. In video-on-demand systems a user may select a program for viewing at any arbitrary time. In near video-on-demand systems, a user is typically given a choice of programming available at repeated specific times. Furthermore, broadcast video applies to programming that occurs with a daily or weekly schedule and is delivered to a wide number of subscribers at the same time.
The video programming can be delivered to a receiver via a number of methodologies, for example but not limited to, satellite, cable, fiber optic technology, etc. After receipt of the programming source content, these systems can use fiber optic cabling technology to deliver the video programming received by a digital receiver to the MPEG-2 digital video broadcast (DVB) equipment. DVB is a standard based on MPEG-2 that specifies the manner in which MPEG-2 data are transmitted via satellite, cable and terrestrial broadcast channels. The MPEG-2/DVB equipment then distributes the video programming via any of a number of methodologies to various locations for distribution to subscribers. Such a distribution system for video programming is described in the above-referenced commonly assigned, co-pending U.S. patent application Ser. No. 09/185,956, entitled SYSTEM AND METHOD FOR THE DELIVERY OF DIGITAL VIDEO AND DATA OVER A COMMUNICATIONS CHANNEL.
The MPEG-2/DVB equipment is capable of receiving the video information at the DVB-asynchronous serial interface (ASI) communication rate of approximately 213 megabits per second (Mbps). However, in the case of satellite delivery of the video content to a digital receiver, the satellite transponder is capable of delivering a data rate less than the 213 Mbps rate that the DVB-ASI equipment is capable of processing. For example, the satellite delivery system may be capable of delivering a data rate in the range of 18-60 Mbps, and typically delivers a data rate of approximately 40 Mbps. This leads to a number of digital receivers each receiving a transport stream at less than the 213 Mbps data rate from a number of satellite transponders. Each transport stream comprises a number of data packets. Because the DVB-ASI standard allows up to approximately a 213 Mbps data rate, and some MPEG-2/DVB equipment is capable of processing the 213 Mbps data stream, it would be desirable to have a way in which to aggregate the lower rate transport streams received from the satellite into a single higher rate transport stream for transfer to a single MPEG-2/DVB device.
Unfortunately, when multiplexing several disparate data packet sources into one higher speed aggregate channel, some data packets will likely be delayed longer than others while waiting to be sent. An MPEG-2 transport stream contains timing sensitive no information in the form of a program clock reference (PCR) value periodically stored in certain transport packets. Timing jitter caused by this multiplexing delay dilutes the accuracy of the PCR value.
Therefore, there is a need in the industry for a manner in which to maximize the bandwidth efficiency of the aforementioned DVB-ASI communication link, while preventing the loss of the timing information contained in the PCR value.
The present invention provides a system and method for maximizing bandwidth efficiency when transporting a number of video signals.
Briefly, in architecture, the system can be described as a system for combining a plurality of video streams into one aggregate video stream, comprising a synchronizer for synchronizing a plurality of video streams to a common clock, a compactor for compacting each valid packet contained in each of the plurality of video streams, a filter for filtering any packets in each of the plurality of video streams that contain null information, and a mixer for combining each of the plurality of compacted, filtered, video streams into an aggregate video stream, the aggregate video stream having a rate at least as great as the combined rate of each of the plurality of video streams.
The present invention can also be viewed as a method for combining a plurality of video streams into one aggregate video stream, the method comprising the steps of synchronizing a plurality of video streams to a common clock, compacting each valid packet contained in each of the plurality of video streams, filtering any packets in each of the plurality of video streams that contain null information, and combining each of the plurality of compacted, filtered, video streams into an aggregate video stream, the aggregate video stream having a rate at least as great as the combined rate of each of the plurality of video streams.